It is generally known in the art that an optical waveguide can be created by placing layers of materials in contact with each other which have different indices of refraction such that light focused in the layer of material having the higher index of refraction will remain in that layer due to total internal reflection of the light at the boundaries between the higher index of refraction material and the materials having lower indices of refraction. There are several patents which teach this general concept. For example, Sugano et al., U.S. Pat. No. 4,015,893, discloses a method for creating light transmission paths on a compound semiconductor surface. Isolation zones are formed on the surface of a substrate by plasma oxidation which causes an oxide film having a different refractive index than the substrate to be selectively formed thereon. The refractive index of the isolation zones gradually decreases from the boundary face between the substrate and the film toward the outer surface of the film. These isolation zones constitute the light transmission paths.
Sugano et al, also disclose epitaxially growing a GaAS0.6P0.4 compound semiconductor layer on a GaAs substrate forming the isolation zones in the GaAS0.6P0.4 layer such that the isolation zones arrive at the GaAs substrate. The refractive index of the oxide film gradually decreases laterally away from the GaAS0.6P0.4 channels such that light entering the oxide film propagates into the GaAS0.6P0.4 channel.
Spillman, Jr., et al., U.S. Pat. No. 4,547,262, disclose a method for fabricating optical waveguides in LiTaO3. A masking pattern is first formed on the surface of the substrate, the substrate surface having the masking pattern thereon is immersed in benzoic acid whereby a proton exchange process occurs which increases the extraordinary component of the refractive index in the unmasked area of the substrate. The substrate is then heated to transform the step index profile produced by the benzoic acid reaction into a gradient index profile having a lowered value of refractive index at the guide surface. The unmasked, altered areas of the substrate comprise the optical waveguides. Spillman Jr., et al. also disclose forming optical elements such as lenses, mirrors, prisms, and diffraction gratings in the planar waveguide formed by the above-discussed method.
Suzuki et al., U.S. Pat. No. 4,983,499, disclose a method for forming a lens in a planar optical waveguide. The planar waveguide is covered with a layer of photoresist which is exposed through a photo mask and developed to form the photoresist mask. The mask has a multiplicity of separate openings and the density of openings per unit area is continuously varied. A material such as titanium is then deposited on the non-masked areas of the surface of the waveguide. The masking positions of the photoresist are then removed thereby leaving only selected areas of the waveguide covered with titanium. The titanium is then thermally diffused into the waveguide to produce a gradient refractive index region in the waveguide which corresponds to the lens.
In another embodiment, Suzuki et al, disclose depositing the titanium layer onto the surface of the waveguide and depositing a layer of photoresist on top of the titanium. The photoresist is masked, exposed and developed thereby leaving openings in the photoresist layer, the density of the openings per unit area being continuously varied. The exposed titanium is etched and the remaining photoresist is subsequently removed, thereby leaving selected areas of the waveguide covered with titanium. The titanium is then diffused into the waveguide to form a gradient refractive index region which corresponds to the lens.
Although the concept of creating optical waveguides and forming optical components in the waveguides is generally known, a need exists in the art for an optical waveguide that can be relatively easily and inexpensively produced.
The process of creating a gradient refractive index area in a material is not, in and of itself, new. For example, Borrelli, et al., U.S. Pat. No. 4,403,031, disclose a method for forming optical patterns in glass by creating optical density and/or refractive index variation in porous glass. The patterns are formed by impregnating a portion of the porous glass with a photolyzable organometallic compound and exposing at least the impregnated portion to photolyzing light to cause photolytic decomposition of the organometallic compound to a photolyzed metal-organic intermediate in a pattern corresponding to the exposure. As discussed above, Spillman, Jr., et al. utilize a proton exchange process to increase the extraordinary component of the refractive index in the unmasked area of a substrate. Once the substrate is heated, the step index profile is transformed into a gradient index profile having a lower value of refractive index at the waveguide surface. Suzuki, et al supra, disclose altering the index of refraction of selected areas of the waveguide by thermally diffusing titanium into the waveguide to produce a gradient refractive index region in the waveguide which corresponds to the lens.
None of the above prior art teaches or suggests forming an optical waveguide from at least two polymer layers which have different indices of refraction. Also, none of the prior art teaches or suggests creating optical elements in a waveguide by methods similar to those of the present invention. Furthermore, none of the prior teaches or suggests fabricating a master waveguide having shaped optical elements formed therein and producing polymer optical waveguides from the master. Moreover, none of these references teach or suggest piercing ¼ wavelength diameter, or smaller, holes into the surface of a polymer layer to create a gradient refractive index lens or other optical element, as is taught by the present invention.